Architecting a VMware NSX Solution : Design Considerations : 4.6 NSX Controller Cluster
   
4.6 NSX Controller Cluster
VMware NSX Controller instances are typically deployed to the NSX Edge cluster and are responsible for the following functions:
Responsible for the switching and routing modules in the hypervisors
Remove the VXLAN dependency on multicast routing/PIM in the physical network
Provide suppression of ARP broadcast traffic in VXLAN networks
Provide the control plane to distribute network information to ESXi hosts
Are clustered for scale-out and high availability